Flame resistant filaments of acrylonitrile polymer

ABSTRACT

A process for preparing flame resistant filaments of acrylonitrile polymer containing at least 40 weight percent acrylonitrile polymer units and at least 15 weight percent vinyl chloride polymer units. The polymer is dissolved in hot dimethylformamide solvent for extrusion into filaments and antimony oxide is dispersed in the solution to enhance the flame resistance of the filaments produced. Zinc oxide or other zinc compound is dispersed in the solution to prevent objectionable deposits of metallic antimony in extrusion equipment.

United States P2 Neal [ FLAME RESISTANT FILAMENTS OF ACRYLONITRILE POLYMER [75] Inventor: Louisa Warnell Neal, Waynesboro,

E. I. du Pont de Nemours and Company, Wilmington, Del.

Filed: Mar. 6, 1974 Appl. No.: 448,687

[73] Assignee:

[52] US. Cl. 260/32.6 N; 106/15 FP;

260/4575 B; 260/4575 W Int. Cl. C08k 1/06; C08f 45/56 Field of Search 260/326 N, 45.75 B,

45.75 W; 106/15 PP References Cited UNITED STATES PATENTS 6/1955 Lally 260/4575 12/1959 Elliott 260/4575 W 5/1963 Tarkington et a1. 260/4575 11/1967 Cheapc, Jr. ct al..... 260/326 7/1968 Mazzocini et 260/328 2/1971 Schwarcz et al. 106/15 FP X 4/1971 Harrington 1 260/25 9/1971 Trapasso ct al 260/326 N Sept. 2, 1975 3,657,179 4/1972 Yates 260/326 N 3,686,112 8/1972 Vrancken ct a1. 260/326 N 3,718,615 2/1973 Woods ct a1. 106/15 FP 3,741,893 6/1973 Mascioli et a1. 106/15 FP 3,770,577 11/1973 Humphrey 106/15 FP OTHER PUBLICATIONS Lyons, The Chem. and Uses of Fire Retardants, pp. 312-316 (Wileylnterscience, 1970) [TP265 L8].

Primary Examiner-Morris Liebman Assistant ExaminerT. DeBenedictis, Sr.

[ 5 7 ABSTRACT 4 Claims, No Drawings FLAME RESISTANT FILAMENTS OF ACRYLONITRILE POLYMER BACKGROUND OF THE INVENTION This invention relates to production of filaments of acrylonitrile polymer and is more particularly concerned with imparting flame resistance.

It has become increasingly important to provide acrylonitrile fibers which are difficult to ignite and burn. In the United States and some other countries, childrcns sleepwear is required by law to be flame resistant. There is also a demand for flame-resistant fibers for other uses, including carpets, drapes, blankets and wearing apparel other than sleepwear. Improved flame resistance is provided by copolymers of acrylonitrile containing vinyl chloride polymer units. The flame resistance of such acrylonitrile polymers is enhanced by the presence of antimony oxide. When filaments are prepared by dissolving acrylonitrile polymer in hot dimethylformamide solvent, extruding the polymer solution to form filaments and then removing the solvent from the filaments. part of any antimony oxide dispersed in a solution of chlorine-containing acrylonitrile polymer is reduced to metallic antimony. This phenomenon occurs within the time periods normally required for processing polymer solutions for extrusion, and is accelerated by the presence of iron alloys and other metals normally used in extrusion equipment. The resulting formation of antimony deposits in the extrusion equipment. especially in pack screens and spinnerets used to form filaments, has impeded attempts to use antimony oxide for flame resistance.

SUMMARY OF THE INVENTION The present invention is an improvement in the process of preparing flame-resistant filaments of acrylonitrile polymer containing at least 40 weight percent ac rylonitrile polymer units and at least weight percent vinyl chloride by dissolving the polymer in hot dimeth ylformamide solvent, extruding the polymer solution to form filaments and removing the solvent from the filaments. The improvement of the present invention provides for use of antimony oxide (Sb O as a flameretardant additive without causing objectionable deposits in fiber-spinning equipment and without adverse effect on desirable fiber properties. Other advantages of the invention will become apparent hereinafter.

In accordance with the present invention, after prc paring the spinning solution of acrylonitrile polymer in hot dimethylformamide solvent, about 1 to 5 parts anti mony oxide per 100 parts by weight of polymer is dispersed in the polymer solution and an amount ofa zinc compound which provides at least 0.1 part zinc per 100 parts by weight of polymer is dispersed in the polymer solution to prevent objectionable deposits of metallic antimony in the fiber-spinning equipment. Any compound of zinc may be employed for this purpose, but zinc oxide is especially preferred. Other preferred zinc compounds include zinc salts of weak acids, such as Zinc carbonate. An amount of zinc compound which provides in excess of 2 parts Zinc per 100 parts by weight of polymer is not required and may be excessive. The antimony oxide is preferably of fine particle size, usually in the range of about 0.05 to 5 microns.

The essential components of an especially preferred fiber-forming composition are (a) a solution in hot dimethylformamide solvent of 100 parts by weight of a terpolymer of about 65 weight percent acrylonitrile, about 33 weight percent vinyl chloride and about 2 weight percent of the triamylamine salt of 2- acrylamido-2-methylpropanesulfonic acid; (b) about 3 parts by weight of antimony oxide having a particle size of about 2 to 4 microns; and (c) about 0.25 to 0.5 parts by weight of zinc oxide. The composition may also include other ingredients conventionally used in acrylonitrile fibers, c.g., delusterants.

DESCRIPTION OF THE INVENTION The polymers to which the process of the present invention are applicable are chlorine-containing acrylonitrile polymers which contain at least 40 weight percent acrylonitrile monomer units and at least 15 weight percent vinyl chloride monomer units. The chlorinecontaining acrylonitrile polymer may include additional monomer units such as styrene, methyl acrylate, methyl methacrylate, and vinyl acetate. Sulfonatecontaining monomers may also be present, preferably in small amounts to impart improved dyeability. In a highly preferred embodiment, the polymer comprises at least 40 weight percent acrylonitrile, at least l5 weight percent vinyl chloride, and about 1 or 2 weight percent of sulfonate-containing monomer. The polymers should be essentially linear, since nonlinear polymers (i.e., cross-linked polymers) are generally not soluble.

A specific instance of a polymer to which the process of the present invention is applicable is given by Jones in Example III of his U.S. Pat. No. 3,748,302. This polymer comprises an acrylonitrile/vinyl chloride/sodium styrenesulfonate terpolymer in the ratio of about 74/25/1 by weight. Other preferred polymers include acrylonitrile/vinyl chloride/Z-acrylamido-Z-methyIpropanesulfonic acid terpolymer in the ratio of about 69/30/1 by weight, prepared as described by LaCombe, et el., in Canadian Pat. No. 704,778; as well as the analogous terpolymer in sodium salt form, acrylonitrile/vinyl chloride/sodium 2mcthacrylamido-2-methylpropanesulfonate terpolymer in the ratio of about 68/30.5/1.5 by weight; and the analogous tertiary amine salt, acrylonitrile/vinyl chloride/triamylammonium 2-acrylamido-2-methylpropanesulfonate terpolymer in the ratio of 65/33/2.

The solution of the chlorine-containing acrylonitrile polymer in dimethylformamide is carried out in conventional manner by stirring the polymer into the solvent. A considerable degree of heating is usually engendered by the mechanical agitation, and an external source of heat may be employed if heating to a higher temperature is desired. Antimony oxide is then dispersed in the solution in an amount sufficient to enhance the flame resistance of the polymer to the desired degree. As previously known, the chorine contained in the polymer and the antimony oxide act together synergistically to provide flame resistance in the fiber product. Usually about l5% of the antimony oxide is added, based on the weight of the polymer. The antimony oxide is preferably of fine particle size, usually in the range of about 0.05 5 microns. If desired, the anitmony oxide may be dispersed in the dimethylformamide first and the polymer dissolved subsequently.

Any compound of zinc may be dispersed with the antimony oxide in the hot solution of the chlorinecontaining acrylonitrile polymer in dimethylformamide. Zinc oxide is very effective and is highly preferred. Other suitable compounds include zinc borate, zinc carbonate, zinc acetate, zinc laurate, zinc benzoate, and other zinc salts of weak acids, as well as zinc hydroxide, zinc chloride, and zinc sulfate. The zinc compounds should be added in an amount sufficient to provide at least 0.1 percent by weight of zinc. Amounts in excess of 2 weight percent of zinc are not required and may be excessive.

The following examples will illustrate the invention. All parts and percentages are expressed on a weight basis unless otherwise indicated.

EXAMPLE I To 32 ml. of dimethylformamide in a glass bottle is added 1.2 ml. of water, with stirring. Then 15 g. of the terpolymer of acrylonitrile (65%), vinyl chloride (33%), and the triamylamine salt of 2-acrylamido-2- methylpropanesulfonie acid (2%) is added slowly, with stirring. The stirring is sufficiently vigorous that the temperature rises to approximately 60C. Next, 0.45 g. (3% by weight, based on polymer) of antimony oxide having a particle size of about 2 to 4 microns is added with continued stirring. The resulting mixture is white and opaque. In this control experiment, no zinc compound is added. A stream of nitrogen is employed to flush air out of the bottle. after which the bottle is closed and the mixture is heated to 120C. and maintained at that temperture. After 21 hours, it is observed that the wall of the bottle has become gray in color, attributable to the deposition of antimony metal upon the wall.

The experiment is repeated, except that 0.045 g. of zinc oxide (0.3 wt. ZnO or 0.24 wt. Zn, based on polymer) is added to the bottle together with the antimony oxide. The bottle containing the mixture is flushed with nitrogen, closed, heated to 120C, and maintained at that temperature. Not until 30 hours have elapsed does a gray color become observable upon the wall of the bottle.

The experiment is repeated once more, except that 0.075 g. of zinc oxide (0.5 wt. 71 ZnO or 0.4 wt. Zn, based on polymer) is added to the bottle together with the antimony oxide. The bottle containing the mixture is flushed with nitrogen, closed, heated to 120C, and maintained at that temperature. The first appearance of gray color upon the wall of the bottle is observed after about 30 hours of heating.

The results of the experiment are summarized in the following table:

Elapsed Time Until Appearance Wt. "/1 Zinc Oxide of Deposited Antimony None (control) 21 hours 0.3% 30 hours 0.57: 30 hours EXAMPLE 11 having a particle size of about 2 to 4 microns is added with continued stirring. A small strip of stainless steel is then placed in the mixture in the bottle. The resulting mixture is white and opaque. In this control experiment, no zinc compound is added. A stream of nitrogen is employed to flush air out of the bottle, ater which the bottle is capped and heated to C. and maintained at that temperature for 24 hours. A heavy black deposit is observed upon the wall of the bottle, attributable to the deposition of antimony metal.

The experiment is repeated, except that 0.35 g. of zinc oxide (0.5 wt. 7c ZnO or 0.4 wt. Zn, based on polymer) is added to the bottle together with the antimony oxide. The bottle containing the mixture is flushed with nitrogen, closed, heated to 120C., and maintained at that temperature for 24 hours. At the end of the heating period almost no deposit is present upon the wall of the bottle.

The experiment is repeated once more, adding 0.17 g. of zinc oxide (0.25 wt. ZnO or 0.2 wt. Zn, based on polymer) to the bottle together with the antimony oxide and subjecting the bottle to the procedure described above. At the end of the 24-hour heating period a small gray deposit is observed upon the wall of the bottle, more than that obtained in the test using 0.5% ZnO above but far less than the heavy deposit obtained in the control experiment with no added zinc compound.

The experiment is repeated still one more time, adding 2.0 g. of zinc laurate (2.85 wt. zinc laurate or 0.4 wt. Zn, based on polymer) to the bottle together with the antimony oxide and subjecting the bottle to the procedure described above. At the end of the 24-hour heating period a considerable gray deposit is observed upon the wall of the bottle. more than those obtained in the tests using zinc oxide but less than the heavy deposit obtained in the control experiment with no added Zine compound.

EXAMPLE 111 To 32 ml. of dimethylformamide in a glass bottle is added 1.6 ml. of water, with stirring. Then 15 g. of the terpolymer of acrylonitrile (65%), vinyl chloride (33%), and the triamylamine salt of 2-acrylamido-2- methylpropanesulfonic acid (2%) is added slowly, with stirring. The stirring is sufficiently vigorous that the temperature rises to approximately 60C. Next, 0.45 g. (3% by weight, based on polymer) of antimony oxide having a particle size of 2 to 4 microns is added with continued stirring. The resulting mixture is white and opaque. Finally, 0.06 g. of zinc carbonate (0.4 wt. ZnCO or 0.2 wt. Zn, based on polymer) is added to the bottle and stirred into the mixture. The bottle containing the mixture is flushed with nitrogen, closed, heated to 120C., and maintained at that temperature. Not until 33 hours have elapsed does a gray color become observable on the wall of the bottle. As noted in Example 1, a gray color is observable after only 21 hours when no zinc compound is added to the mixture.

The experiment is repeated, employing 0.09 g. of zinc carbonate (0.6 wt. ZnCO or 0.3 wt. Zn, based on polymer). The same result is obtained, with a gray color becoming observable upon the wall of the bottle after 33 hours. In other experiments, the gray color becomes observable in slightly less time: 26 hours when 0.075 g. of zinc carbonate (0.5 wt. 7: ZnCO or 0.25 wt. Zn, based on polymer) is used and 27 hours when 0.105 g. of zinc carbonate (0.7 wt. ZnCO or 0.35 wt. 7! Zn, based on polymer) is used.

I claim:

1. In the process of preparing flameresistant filaments of acrylonitrile polymer containing at least 40 weight percent acrylonitrile polymer units and at least weight percent vinyl chloride polymer units by dis solving the polymer in hot dimethylformamide solvent, extruding the polymer solution to form filaments and removing the solvent from the filaments; the improvement which comprises dispersing in the polymer solution about 1 to 5 parts antimony oxide per 100 parts by weight of polymer and about 0.25 to 0.5 part of zinc oxide per 100 parts by weight of polymer to prevent objectionable deposits of metallic antimony.

2. A fiber-forming acrylonitrile polymer composition consisting essentially of (a) a solution in hot dimethylformamide solvent of an acrylonitrile polymer which contains at least 40 weight percent acrylonitrile polymer units and at least 15 weight percent vinyl chloride polymer units, (b) l to 5 parts antimony oxide per parts by weight of polymer, dispersed in said solution, and (c) about 0.25 to 0.5 part of zinc oxide per 100 parts by weight of polymer, dispersed in said solution to prevent objectionable deposits of metallic antimony.

3. The composition defined in claim 2 wherein the antimony oxide is of a particle size within the range of about 0.05 to 5 microns.

4. The composition as defined in claim 2 and consisting essentially of (a) a solution in hot dimethylformamide solvent of 100 parts by weight of a terpolymer of about 65 weight percent acrylonitrile, about 33 weight percent vinyl chloride and about 2 weight percent of the triamylamine salt of 2-aerylamido-2- methylpropanesulfonic acid; (b) about 3 parts by weight of antimony oxide having a particle size of about 2 to 4 microns; and (c) about 0.25 to 0.5 parts by 

1. IN THE PROCESS OF PREPARING FLAME-RESISTANT- FILAMENTS OF ACRYLONITRILE POLYMER CONTANING AT LEAST 40 WEIGHT PERCENT ACRYLONITRILE POLYMER UNITS AND AT LEAST 15 WEIGHT PERCENT VINYL CHLORIDE POLYMER UNITS BY DISSOLVING THE POLYMER IN HOT DIMETHYLFORMAMIDE SOLVENT EXTRUDING THE POLYMER SOLUTION TO FORM FILAMENTS REMOVING THE SOLVENT FROM THE FILAMENTS THE IMPROVEMENT WHICH COMPRISES DISPERSING IN THE POLYMER SOLUTION ABOUT 1 TO 5 PARTS ANTIMONY OXIDE PER 100 PARTS BY WEIGHT OF POLYMER AND ABOUT 0.25 TO 0.5 PARTS OF ZINC OXIDE PER 100 PARTS BY WEIGHT OF POLYMER TO PREVENT OBJECTIONABLE DEPOSITS OF METALLIC ANTIMONY.
 2. A fiber-forming acrylonitrile polymer composition consisting essentially of (a) a solution in hot dimethylformamide solvent of an acrylonitrile polymer which contains at least 40 weight percent acrylonitrile polymer units and at least 15 weight percent vinyl chloride polymer units, (b) 1 to 5 parts antimony oxide per 100 parts by weight of polymer, dispersed in said solution, and (c) about 0.25 to 0.5 part of zinc oxide per 100 parts by weight of polymer, dispersed in said solution to prevent objectionable deposits of metallic antimony.
 3. The composition defined in claim 2 wherein the antimony oxide is of a particle size within the range of about 0.05 to 5 microns.
 4. The composition as defined in claim 2 and consisting essentially of (a) a solution in hot dimethylformamide solvent of 100 parts by weight of a terpolymer of about 65 weight percent acrylonitrile, about 33 weight percent vinyl chloride and about 2 weight percent of the triamylamine salt of 2-acrylamido-2-methylpropanesulfonic acid; (b) about 3 parts by weight of antimony oxide having a particle size of about 2 to 4 microns; and (c) about 0.25 to 0.5 parts by weight of zinc oxide. 